Dialysis involves connecting patients with insufficient kidney function to a dialysis machine which cleanses the blood of waste products and impurities. Put another way, the dialysis machine performs the same function as a normal, healthy kidney should. In other cases, dialysis is used to remove poisons and drugs from the blood more safely and quickly than the natural kidneys would. To properly connect a patient to a dialysis machine requires accessing, on a continuing basis, a blood vessel, to divert the flow of blood from the patient to the dialysis machine. This is normally accomplished by the implantation into the patient of an artificial fistula or bypass graft, which is usually made of expanded polytetrafluoroethylene (ePTFE). In the case of a graft, the graft is punctured with a needle and blood from patients requiring dialysis is transported to the dialysis machine whereupon the blood is diffused across a semipermeable membrane. Upon completion of this procedure, dialyzed blood is returned to the patient through a second needle in the graft. Dialysis is usually necessary every two to three days, which often results in the lumen of the graft becoming compromised. The more common problem related to dialysis grafts is intimal hyperplasia, which can occur when the higher pressure/volume of the arterial flow crosses the boundary from the relatively non-compliant graft to the more compliant outflow vein at the venous anastomosis. The resultant intimal hyperplasia in the vein adjacent to the anastomosis leads to progressive stenosis and eventually premature clotting and graft occlusion. Repairing a hemodialysis graft occlusion is currently accomplished by one of several techniques: open surgical revision (surgical thrombectomy), thrombolytic drugs (thrombolysis) or mechanical declotting via percutaneous techniques (percutaneous mechanical thrombectomy). Percutaneous mechanical thrombectomy techniques include suction thrombectomy, balloon thrombectomy, clot maceration and mechanical thrombectomy. The goal of each of these therapies is the preservation of vascular access. In almost all cases, any technique which is used to declot the graft will also require angioplasty of the venous anastomotic stenosis in order to reestablish normal flow.
It is known that blood flow in excess of 300 cc per minute can cause intimal hyperplasia in the outflow vein near the anastomosis. The problem arises from the fact that blood flows less than 300 cc per minute have been associated with graft thrombosis. The solution to this dilemma appears to arise from a recognition that blood flows of less than 300 cc per minute are not intrinsically pro-thrombotic, but are a reflection of progressive stenosis that is likely to rapidly reach a level at which thrombosis can occur with any added insult. What would be ideal and what is clearly needed is a method for preventing high flows through the graft while it is not being used and thus reducing or eliminating the stimulus for intimal hyperplasia and yet allowing the high flows through the graft during dialysis that are required for a successful dialysis run.